Update merge on refresh and merge on commit defaults in Opensearch (L…

…ucene 9.3) (#3561) (#4013)

* Update merge on refresh and merge on commit defaults in Opensearch (Lucene 9.3)

Signed-off-by: Andriy Redko <andriy.redko@aiven.io>

* Addressing code review comments, adding more tests

Signed-off-by: Andriy Redko <andriy.redko@aiven.io>
(cherry picked from commit a34a4c0)
Signed-off-by: Andriy Redko <andriy.redko@aiven.io>

server/src/main/java/org/opensearch/common/settings/IndexScopedSettings.java

@@ -193,6 +193,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
                 ExistingShardsAllocator.EXISTING_SHARDS_ALLOCATOR_SETTING,
                 IndexSettings.INDEX_MERGE_ON_FLUSH_ENABLED,
                 IndexSettings.INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME,
+                IndexSettings.INDEX_MERGE_ON_FLUSH_POLICY,
 
                 // validate that built-in similarities don't get redefined
                 Setting.groupSetting("index.similarity.", (s) -> {

server/src/main/java/org/opensearch/index/IndexSettings.java

@@ -32,11 +32,12 @@
 package org.opensearch.index;
 
 import org.apache.logging.log4j.Logger;
-import org.apache.logging.log4j.util.Strings;
 import org.apache.lucene.index.MergePolicy;
+import org.apache.lucene.sandbox.index.MergeOnFlushMergePolicy;
 import org.opensearch.LegacyESVersion;
 import org.opensearch.Version;
 import org.opensearch.cluster.metadata.IndexMetadata;
+import org.opensearch.common.Strings;
 import org.opensearch.common.logging.Loggers;
 import org.opensearch.common.settings.IndexScopedSettings;
 import org.opensearch.common.settings.Setting;
@@ -53,9 +54,11 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.UnaryOperator;
 
 import static org.opensearch.index.mapper.MapperService.INDEX_MAPPING_DEPTH_LIMIT_SETTING;
 import static org.opensearch.index.mapper.MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING;
@@ -73,6 +76,9 @@
  * @opensearch.internal
  */
 public final class IndexSettings {
+    private static final String MERGE_ON_FLUSH_DEFAULT_POLICY = "default";
+    private static final String MERGE_ON_FLUSH_MERGE_POLICY = "merge-on-flush";
+
     public static final Setting<List<String>> DEFAULT_FIELD_SETTING = Setting.listSetting(
         "index.query.default_field",
         Collections.singletonList("*"),
@@ -515,14 +521,21 @@ public final class IndexSettings {
     public static final Setting<TimeValue> INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME = Setting.timeSetting(
         "index.merge_on_flush.max_full_flush_merge_wait_time",
         new TimeValue(10, TimeUnit.SECONDS),
-        new TimeValue(0, TimeUnit.MILLISECONDS),
+        new TimeValue(1, TimeUnit.MILLISECONDS),
         Property.Dynamic,
         Property.IndexScope
     );
 
     public static final Setting<Boolean> INDEX_MERGE_ON_FLUSH_ENABLED = Setting.boolSetting(
         "index.merge_on_flush.enabled",
-        false,
+        true, /* https://issues.apache.org/jira/browse/LUCENE-10078 */
+        Property.IndexScope,
+        Property.Dynamic
+    );
+
+    public static final Setting<String> INDEX_MERGE_ON_FLUSH_POLICY = Setting.simpleString(
+        "index.merge_on_flush.policy",
+        MERGE_ON_FLUSH_DEFAULT_POLICY,
         Property.IndexScope,
         Property.Dynamic
     );
@@ -617,6 +630,10 @@ private void setRetentionLeaseMillis(final TimeValue retentionLease) {
      * Is merge of flush enabled or not
      */
     private volatile boolean mergeOnFlushEnabled;
+    /**
+     * Specialized merge-on-flush policy if provided
+     */
+    private volatile UnaryOperator<MergePolicy> mergeOnFlushPolicy;
 
     /**
      * Returns the default search fields for this index.
@@ -733,6 +750,7 @@ public IndexSettings(final IndexMetadata indexMetadata, final Settings nodeSetti
         mappingFieldNameLengthLimit = scopedSettings.get(INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING);
         maxFullFlushMergeWaitTime = scopedSettings.get(INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME);
         mergeOnFlushEnabled = scopedSettings.get(INDEX_MERGE_ON_FLUSH_ENABLED);
+        setMergeOnFlushPolicy(scopedSettings.get(INDEX_MERGE_ON_FLUSH_POLICY));
 
         scopedSettings.addSettingsUpdateConsumer(MergePolicyConfig.INDEX_COMPOUND_FORMAT_SETTING, mergePolicyConfig::setNoCFSRatio);
         scopedSettings.addSettingsUpdateConsumer(
@@ -804,6 +822,7 @@ public IndexSettings(final IndexMetadata indexMetadata, final Settings nodeSetti
         scopedSettings.addSettingsUpdateConsumer(INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING, this::setMappingFieldNameLengthLimit);
         scopedSettings.addSettingsUpdateConsumer(INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME, this::setMaxFullFlushMergeWaitTime);
         scopedSettings.addSettingsUpdateConsumer(INDEX_MERGE_ON_FLUSH_ENABLED, this::setMergeOnFlushEnabled);
+        scopedSettings.addSettingsUpdateConsumer(INDEX_MERGE_ON_FLUSH_POLICY, this::setMergeOnFlushPolicy);
     }
 
     private void setSearchIdleAfter(TimeValue searchIdleAfter) {
@@ -874,7 +893,7 @@ public String getUUID() {
      * Returns <code>true</code> if the index has a custom data path
      */
     public boolean hasCustomDataPath() {
-        return Strings.isNotEmpty(customDataPath());
+        return !Strings.isEmpty(customDataPath());
     }
 
     /**
@@ -1390,4 +1409,27 @@ public TimeValue getMaxFullFlushMergeWaitTime() {
     public boolean isMergeOnFlushEnabled() {
         return mergeOnFlushEnabled;
     }
+
+    private void setMergeOnFlushPolicy(String policy) {
+        if (Strings.isEmpty(policy) || MERGE_ON_FLUSH_DEFAULT_POLICY.equalsIgnoreCase(policy)) {
+            mergeOnFlushPolicy = null;
+        } else if (MERGE_ON_FLUSH_MERGE_POLICY.equalsIgnoreCase(policy)) {
+            this.mergeOnFlushPolicy = MergeOnFlushMergePolicy::new;
+        } else {
+            throw new IllegalArgumentException(
+                "The "
+                    + IndexSettings.INDEX_MERGE_ON_FLUSH_POLICY.getKey()
+                    + " has unsupported policy specified: "
+                    + policy
+                    + ". Please use one of: "
+                    + MERGE_ON_FLUSH_DEFAULT_POLICY
+                    + ", "
+                    + MERGE_ON_FLUSH_MERGE_POLICY
+            );
+        }
+    }
+
+    public Optional<UnaryOperator<MergePolicy>> getMergeOnFlushPolicy() {
+        return Optional.ofNullable(mergeOnFlushPolicy);
+    }
 }

server/src/main/java/org/opensearch/index/engine/InternalEngine.java

@@ -50,7 +50,6 @@
 import org.apache.lucene.index.ShuffleForcedMergePolicy;
 import org.apache.lucene.index.SoftDeletesRetentionMergePolicy;
 import org.apache.lucene.index.Term;
-import org.apache.lucene.sandbox.index.MergeOnFlushMergePolicy;
 import org.apache.lucene.search.BooleanClause;
 import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -133,6 +132,7 @@
 import java.util.function.BiFunction;
 import java.util.function.LongConsumer;
 import java.util.function.LongSupplier;
+import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -2448,14 +2448,14 @@ private IndexWriterConfig getIndexWriterConfig() {
             final long maxFullFlushMergeWaitMillis = config().getIndexSettings().getMaxFullFlushMergeWaitTime().millis();
             if (maxFullFlushMergeWaitMillis > 0) {
                 iwc.setMaxFullFlushMergeWaitMillis(maxFullFlushMergeWaitMillis);
-                mergePolicy = new MergeOnFlushMergePolicy(mergePolicy);
-            } else {
-                logger.warn(
-                    "The {} is enabled but {} is set to 0, merge on flush will not be activated",
-                    IndexSettings.INDEX_MERGE_ON_FLUSH_ENABLED.getKey(),
-                    IndexSettings.INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME.getKey()
-                );
+                final Optional<UnaryOperator<MergePolicy>> mergeOnFlushPolicy = config().getIndexSettings().getMergeOnFlushPolicy();
+                if (mergeOnFlushPolicy.isPresent()) {
+                    mergePolicy = mergeOnFlushPolicy.get().apply(mergePolicy);
+                }
             }
+        } else {
+            // Disable merge on refresh
+            iwc.setMaxFullFlushMergeWaitMillis(0);
         }
 
         iwc.setMergePolicy(new OpenSearchMergePolicy(mergePolicy));

server/src/test/java/org/opensearch/common/lucene/LuceneTests.java

@@ -590,10 +590,8 @@ public void testWrapAllDocsLive() throws Exception {
     public void testWrapLiveDocsNotExposeAbortedDocuments() throws Exception {
         Directory dir = newDirectory();
         IndexWriterConfig config = newIndexWriterConfig().setSoftDeletesField(Lucene.SOFT_DELETES_FIELD)
-            .setMergePolicy(new SoftDeletesRetentionMergePolicy(Lucene.SOFT_DELETES_FIELD, MatchAllDocsQuery::new, newMergePolicy()));
-        // override 500ms default introduced in
-        // https://issues.apache.org/jira/browse/LUCENE-10078
-        config.setMaxFullFlushMergeWaitMillis(0);
+            .setMergePolicy(new SoftDeletesRetentionMergePolicy(Lucene.SOFT_DELETES_FIELD, MatchAllDocsQuery::new, newMergePolicy()))
+            .setMaxFullFlushMergeWaitMillis(0);
         IndexWriter writer = new IndexWriter(dir, config);
         int numDocs = between(1, 10);
         List<String> liveDocs = new ArrayList<>();

server/src/test/java/org/opensearch/index/engine/InternalEngineTests.java

@@ -499,8 +499,7 @@ public void testMergeSegmentsOnCommitIsDisabled() throws Exception {
 
         final Settings.Builder settings = Settings.builder()
             .put(defaultSettings.getSettings())
-            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME.getKey(), TimeValue.timeValueMillis(0))
-            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_ENABLED.getKey(), true);
+            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_ENABLED.getKey(), false);
         final IndexMetadata indexMetadata = IndexMetadata.builder(defaultSettings.getIndexMetadata()).settings(settings).build();
         final IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(indexMetadata);
 
@@ -572,7 +571,7 @@ public void testMergeSegmentsOnCommit() throws Exception {
         final Settings.Builder settings = Settings.builder()
             .put(defaultSettings.getSettings())
             .put(IndexSettings.INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME.getKey(), TimeValue.timeValueMillis(5000))
-            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_ENABLED.getKey(), true);
+            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_POLICY.getKey(), "merge-on-flush");
         final IndexMetadata indexMetadata = IndexMetadata.builder(defaultSettings.getIndexMetadata()).settings(settings).build();
         final IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(indexMetadata);
 
@@ -634,14 +633,52 @@ public void testMergeSegmentsOnCommit() throws Exception {
         }
     }
 
+    public void testMergeSegmentsOnCommitDefault() throws Exception {
+        final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
+
+        final Settings.Builder settings = Settings.builder().put(defaultSettings.getSettings());
+        final IndexMetadata indexMetadata = IndexMetadata.builder(defaultSettings.getIndexMetadata()).settings(settings).build();
+        final IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(indexMetadata);
+
+        final TieredMergePolicy mergePolicy = new TieredMergePolicy();
+        mergePolicy.setSegmentsPerTier(2);
+
+        try (
+            Store store = createStore();
+            InternalEngine engine = createEngine(
+                config(indexSettings, store, createTempDir(), mergePolicy, null, null, globalCheckpoint::get)
+            )
+        ) {
+            List<Segment> segments = engine.segments(true);
+            assertThat(segments.isEmpty(), equalTo(true));
+
+            ParsedDocument doc = testParsedDocument("1", null, testDocumentWithTextField(), B_1, null);
+            engine.index(indexForDoc(doc));
+            engine.refresh("test");
+
+            segments = engine.segments(true);
+            assertThat(segments.size(), equalTo(1));
+
+            ParsedDocument doc2 = testParsedDocument("2", null, testDocumentWithTextField(), B_2, null);
+            engine.index(indexForDoc(doc2));
+            engine.refresh("test");
+            ParsedDocument doc3 = testParsedDocument("3", null, testDocumentWithTextField(), B_3, null);
+            engine.index(indexForDoc(doc3));
+            engine.refresh("test");
+
+            segments = engine.segments(true);
+            assertThat(segments.size(), equalTo(2));
+        }
+    }
+
     // this test writes documents to the engine while concurrently flushing/commit
     public void testConcurrentMergeSegmentsOnCommit() throws Exception {
         final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
 
         final Settings.Builder settings = Settings.builder()
             .put(defaultSettings.getSettings())
             .put(IndexSettings.INDEX_MERGE_ON_FLUSH_MAX_FULL_FLUSH_MERGE_WAIT_TIME.getKey(), TimeValue.timeValueMillis(5000))
-            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_ENABLED.getKey(), true);
+            .put(IndexSettings.INDEX_MERGE_ON_FLUSH_POLICY.getKey(), "merge-on-flush");
         final IndexMetadata indexMetadata = IndexMetadata.builder(defaultSettings.getIndexMetadata()).settings(settings).build();
         final IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(indexMetadata);
 

server/src/test/java/org/opensearch/index/shard/ShardGetServiceTests.java

@@ -56,7 +56,6 @@ public void testGetForUpdate() throws IOException {
             .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)
             .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 1)
             .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
-
             .build();
         IndexMetadata metadata = IndexMetadata.builder("test")
             .putMapping("{ \"properties\": { \"foo\":  { \"type\": \"text\"}}}")